Installation of devices into a control system requires wires be connected between the devices and the control system the devices communicate with. The wires supply power and provide for signal generation between the control system and the devices. In these control applications wiring is generally accomplished via one of two methods: insulated wire contained inflexible metal conduit, or by using insulated plenum cable. In either case, the attachment of the flexible metal conduit or the unprotected plenum cable must be secure enough to prevent the power or control signal wires from being accidentally dislodged from wiring terminals.
Flexible metal conduit is usually attached to an electrical housing or enclosure with adapter fittings purchased from an outside supply source. These fittings must be ordered, made available, and require labor to affix them to the housing (or enclosure) and to the flexible metal conduit. The strain-relief for plenum cable (which is somewhat similar to small-diameter to appliance cord) is accomplished via any number of schemes to prevent the protective outer jacket from being displaced or moved relative to the device housing when subjected to moderate pull force. Common methods for providing plenum cable strain-relief may include a maze or labyrinth of pins or barriers internal to the housing of the device which the cable must be threaded through to provide the necessary friction or clamping force against the cable. The problem with such methods is that they necessitate unnecessary procurement, cost and labor, and require too much internal space to provide plenum cable strain relief.
The present invention provides an improved design for securing electrical conductors such as, but not limited to, metal conduit or plenum cable into device housings. This is accomplished via a reversible clamp-strap which can be installed in two different orientations. The first orientation is for affixing flexible metal conduit. The second orientation provides for plenum cable strain-relief. Both orientations basically provide clamping pressure against either the flexible metal conduit or the plenum cable outer jacket. For the flexible metal conduit application, positive retention of the conduit is enhanced by the lanced tabs of the clamp strap which key to the spiral seam of the conduit, and by the actual deformation of the clamp strap itself. Such deformation is controlled by the design gap between screw towers (provided on the base of the device housing) and the clamp strap prior to tightening the screws, which secure the clamp-strap to the screw towers. Plenum cable strain-relief is enhanced by raised grip bars which are internally molded features of the base. The grip bars further secure the outer jacket of the plenum cable as the clamp strap is pressed against it.